Preparing metal surfaces for coating with metals and metal alloys



Patented Oct. 31, 1933 UNITED STATES PATE NT OFFlCE 1,932,113 ranmnmc METAL SURFACES FOR COAT- ING WITH METALS AND METAL ALLOYS tion of Ontario No Drawing. Application November 10, 1931' Serial N0. 574,224

17 Claims.

This invention relates to the. preparation of metal surfaces for coating with metals and metal-1 alloys, and more particularly to a process of preparing the surfaces of ferrous metals for coating 5 with low melting metals and metal alloys.

As is well known; the processes customarily employed for preparing metal surfaces for galvanizing, tin plating and the like, while reasonably satisfactory, are attended with several pracl0 tical disadvantages.

processes are to expensive in operation for economical commercial use. Others do not provide the metal under treatment with a uniform surface. Still others leave so-called pin holes in the metal surfaces with the result that subsequent coating cannot completely protect the surfaces from corrosion.

Because of these disadvantages much efiort has been expended and extensive research conducted in an attempt to provide a wholly. satisfactory commercial process for preparing metal surfaces for subsequent metal-coating. .As a result of the work done along this line numerous new processes of preparing metal surfaces processes, which has attracted some interest, involves the immersing of clean metal surfaces in a strong solution of lead acetate in order to deposit a film of lead on the metal surface as a result of chemical reaction. However this process has not proved to be suitable'for best commercial practice for the reason that the treatment has resulted in a somewhat spangled or spongious coating of lead on the metal due to the fact that the particles of lead deposited on' the metal are relatively large. Moreover, flushing of the surfaces treated by this process with water results in the detachment of some of the lead particles with the result that pin holes are formed in the metal, which is obviously disadvantageous.

The principal object of the present invention is to provide a process of preparingmetal surfaces for coating with metals and metal alloys which overcomes in large measure the disadvantages of the processes heretofore used asset forth above. An important object of the invention is to provide a process of preparing the surfaces of ferrous metals for subsequent coating with corrosion resisting metals andmetal alloys.

Other objects and advantages of the invention will become apparent during the course of the following description.

In the practice of our process the metal to be coated. such as iron or steel, is first pickled by For example, some of the for coating have been proposed. One of theseany conventional pickling process to provide a clean bright surface on the metal. A satisfactory conventional method of preliminarily treating the metal is to-immerse it in 15 'per cent. hydrochloric acid which preferably contains an inhibitor forpreventing pitting and the generation of hydrogen. Any other conventional method which results in a bright pickle may obviously be employed.

After the pickling operation the metal is washed with an excess'of water to remove the pickling solution and is immersed, preferably immediately, in a molten bath of a lead salt of a non-soap forming fatty acid, such as lead propionate or lead acetate, preferably the latter. During the treatment the mass of the lead salt should be maintained at a suflicient temperature to keep the mass in molten'condition. While this temperature may be varied considerably we have found that the process may be advantageously practiced at a temperature of approximately 100 C. As a result of this treatment the metal being treated reacts with the molten lead salt and causes thedeposition of a thin film of lead on the metal surface. In the case where iron is being treated with molten lead acetate, the iron reacts with the leadacetate to' form iron acetate, metallic lead being deposited in a thin coating on the surface of the iron. We have found that the thickness of the lead film on the surface of the iron as a result of this treatment is ordinarily about 0.0001 of an inch. v

The period of treatment may be varied considerably without adversely alfecting the results. The preferred time of treatment under'a particular set of conditions may readily be determined by running a test sheet of metal through the'process and measuring the thickness of the lead film deposited. In preferred practice we speed up the time of operation of the process by adding to the molten lead saltfrom 1 to 5 per cent. by weight of an acid which forms a soluble lead salt in order to increase the hydrogen-ion concentration of the mass. Examples of the acids which may be employed are nitric acid and glacial acetic acid. Our preference isfor glacial acetic acid and we recommend its use. When this acid is employed as an accelerator the time of treatment required is ordinarily about 10 minutes.

After the metal has been immersed in the molten bath for the desired period of time the -.-material is removed from the bath and promptly centrifuged to remove the viscous mass therefrom. Promptly thereafter the thinly coated metal is washed thoroughly with water or with a reasonably strong solution of acetic acid. If an acid wash is used it should be followed by a thorough washing with cold water. Following this washing the metal is in condition to be coated with zinc, cadmium or other low melting metal coating, and particularly the corrosion resisting metal alloy coatings disclosed in our copending application Serial Number 574,225, filed November l0, 1931.

In the event that the metal treated in accordance with the present process is not to be coated promptly with a protective metal coating of the character referred to above, it is important that the treated metal be maintained out of contact with the air or other oxidizing agent. This may advantageously be accomplished by immersing the treated metal in a solution of zinc chloride.

The foregoing process has been demonstrated to be commercially economical and thoroughly practical for use on a commercial scale. Exhaustive tests have demonstrated that metals treated in accordance with the process may readily be provided with corrosion resisting coatings which are far more satisfactory than those ordinarily provided, this being due to the manner in which the metal surfaces have been prepared prior to' the coating.

While we have described in detail the preferred practice of our process it is to be understood that the details of procedure may be variously modified without departing from the spirit of the invention or the scope of the subjoined claims.

We claim:

1. The process of preparing metal surfaces for coating with metals and metal alloys which comprises cleaning the surface of the metal under treatment, and immersing the cleaned metal in a molten bath of a lead salt of a non-soap forming fatty acid. 1

2. The process of preparing metal surfaces for coating with metals and metal alloys which comprises cleaning the surface of the metal under treatment, and immersingthe cleaned metal in a molten bath of lead acetate.

3. The process of preparing metal surfaces for coating with metals and metal alloys which comprises cleaning the surface of the metal under treatment, and immersing the cleaned metal in a molten bath of a lead salt of a non-soap forming fatty acid containing a minor proportion of an acid which forms a soluble lead salt.

4. The process of preparing metal surfaces for coating' with metals and metal alloys which comprises cleaning the surface of the metal under treatment, and immersing the cleaned metal in a molten bath of a lead, salt of a non-soap forming fatty acid containing a minor proportion of glacial acetic acid.

5. The process of preparing metal surfaces for coating with metals and metal alloys which comprises cleaning the surface of the metal under treatment, and immersing the cleaned metal in a molten bath of lead acetate containing a minor proportion of an acid which forms a soluble lead salt.

6. The process of preparing metal surfaces for coating with metals and metal alloys which comprises cleaning the surface of the metal under treatment, and immersing the cleaned metal in a molten bath of lead acetate containing a minor proportion of glacial acetic acid.

'7. The process of preparing the surfaces of ferrous metals for coating with metals and metal alloys which comprises pickling the metal under treatment, and immersing the treated metal in a molten bath of a lead salt of a non-soap forming fatty acid.

8. The process of preparing the surfaces of ferrous metals for coating with metals and metal alloys which comprises pickling the metal under treatment, and immersing the treated metal in a molten bath of lead acetate.

9. The process of preparing .the surfaces of ferrous metals for coating with metals and metal alloys which comprises pickling the metal under treatment, and immersing the treated metal in a molten bath of alead salt of a non-soap forming fatty acid containing a minor proportion of an acid which forms a soluble lead salt.

10. The process of preparing the surfaces of ferrous metals for coating with metals and metal alloys which comprises pickling the metal under treatment, and immersing the treated metal in a molten bath of a lead salt of a non-soap forming fatty acid containing a minor proportion of glacial acetic acid.

11. The process of preparing the surfaces of ferrous metals for coating with metals and metal alloys which comprises pickling the metal under treatment, and immersing the treated metal in a molten bath of lead acetate containing a minor proportion of an acid which forms a soluble lead salt.

12. The process of preparing the surfaces of ferrous metals for coating with metals and metal alloys which comprises pickling the metal under treatment, and immersing the treated metal in a molten bath of lead acetate containing a minor proportion of glacial acetic acid.

13. The process of preparing the surfaces of ferrous metals for coating with metals and metal alloys which comprises pickling the metal under treatment, washing the pickling solution from the metal, immersing the washed metal in a molten bath of a lead salt of a non-soap forming fatty acid, removing the thus treated metal from the molten bath, and washing the surface of the resulting metal.

14. The process of preparing the surfaces of ferrous metals for coating with metals and metal alloys which comprises pickling the metal under treatment, washing the pickling solution from the surface of the metal, immersing the washed metal in a molten bath of lead acetate, removing the metal from the bath, mechanically removcous mass present from the surface of the metal,

and washing the thus treated metal.

16. The process of preparing the surfaces of ferrous metals for coating with metals and metal alloys which comprises subjecting the metal under treatment to the action of a pickling bath to efiect a bright pickle of the metal, washing the resulting metal with an excess of water, immersing the washed metal in a molten bath of lead acetate, removing the thus treated metal 10 minutes in a molten bath of lead acetate containing a minor proportion oi glacial acetic acid; said bath beingmaintained at a temperature of approximately T00 C., removing the thus treated metal from the bath, centrifuging ofi the viscous film from the surface of the metal, and washing the resulting metal first with an acetic acid solution and thereafter with cold water.

FRANCIS H. SNYDER. STANLEY F. M. MACLAREN. 

